1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for expanding a tubular in a wellbore. More particularly, embodiments of the present invention relate to an expandable liner hanger.
2. Description of the Related Art
Hydrocarbon wells are typically formed by drilling a borehole from the earth's surface through subterranean formations to a selected depth in order to intersect one or more hydrocarbon bearing formations. A string of casing is used to line the borehole, and an annular area between the casing and the borehole is filled with cement to further support and form the wellbore.
After the initial string of casing is set, the wellbore is drilled to a new depth. An additional string of casing, or liner, is then run into the well to a depth whereby the upper portion of the liner, is overlapping the lower portion of the surface casing. The liner string is then fixed or hung in the wellbore by a liner hanger. The conventional liner hanger includes a slip system to grip the surrounding casing. One problem associated with the slip system of the conventional liner hanger relates to the relative movement of the parts necessary in order to set the liner hanger in a wellbore. Because the slip system requires parts of the liner hanger to be moved in opposing directions, a run-in tool or other mechanical device must necessarily run into the wellbore with the liner hanger to create the movement. Additionally, the slip system takes up valuable annular space in the wellbore.
Expandable tubular technology has been used to fix a liner string in the wellbore. Expansion technology enables a smaller tubular to be run into a larger tubular, and then radially expanded so that a portion of the smaller tubular (a hanger portion, for instance) is in contact with the larger tubular therearound. Tubulars are expanded by the use of a cone-shaped mandrel or by an expander tool with radially extendable members. During expansion of a tubular, the tubular wall is expanded past its elastic limit and gripping formations on the outer surface of the expandable hanger fix the smaller tubular in the larger diameter tubular.
While expanding tubulars in a wellbore offers obvious advantages, there are problems associated with using the technology to create a hanger through the expansion of one tubular into a surrounding casing. One problem is that the internal diameter of the casing may vary within currently accepted tolerances. For instance, American Petroleum Institute (API) tolerances permit the internal diameter of casing to vary by 0.25″ more or less, depending on the size of the casing. This variation in the internal diameter of the casing can cause a fixed diameter cone to become stuck in the wellbore, if the variation is on the low side. Conversely, this variation in the internal diameter of casing can also cause an inadequate expansion of the tubular in the casing if the variation is on the high side. The result is an inadequate coupling between the tubular and the casing.
Thus, there exists a need for an improved expandable liner hanger that accounts for variations in the internal diameter of casing.